Habitats:

Pollutants:

The relationship between acidity and the species composition of diatoms has been recognised for many decades (e.g. Hustedt 1937-39; Nygaard 1956). They serve as good indicators to changes in environmental parameters such as pH and nutrient availability. They also have short generation times and the community composition reacts relatively quickly to changes in the environmental conditions.

The marked decline of Racomitrium lanuginosum in the southern Pennines since the industrial Revolution (Tallis 1987) may be associated with acid deposition, deposition of sulphate and sulphuric acid in rain and cloud droplets, (Ferguson & Lee 1983a, Thompson & Baddeley 1991). There is also evidence of decline in Scotland where critical loads are exceeded (Fowler et al. 2001). Direct negative effects on mosses are possible with the leaching of base cations from cell membrane s.